Magnetic latching switch having residual magnetism for crosspoint hold means



United States Patent 3,400,225 MAGNETIC LATCHING SWITCH HAVING RESIDUAL MAGNETISM FOR CROSS- POINT HOLD MEANS Edson L. Erwin, Towaco, N.J., assignor to International Telephone & Telegraph Corporation, New York, N.Y., a corporation of Maryland Filed July 13, 1965, Ser. No. 471,574 7 Claims. (Cl. 179-22) ABSTRACT OF THE DISCLOSURE A telecommunication crossbar switching system in which the hold magnet core is driven to saturation by a pulse from a common control device and in which the hold magnet core remains actuated by residual core fiux. Thus, a continuous hold current is unnecessary. At the end of the call a release potential of opposite polarity is applied across the core winding and the crosspoint is opened.

This invention relates to a magnetic latching switch and more particularly to a crossbar switch wherein the crosspoints are held by residual magnetism in the cores of hold magnets.

Crossbar switches are devices having a coordinate array of select and horizontal bars which are selectively operated by the simultaneous energization of select and hold magnets. A set of electrical contacts close at the intersection of two operated bars. Thereafter, the select magnet is de-energized to release the operated select bar, and the hold magnet continues to be energized to hold the crosspoint for the duration of a call. After the call is over, the hold magnet is de-energized and the crosspoint releases. The disadvantage of this operation is that the energized hold magnets require a constant supply of power.

To avoid power dissipation, the prior art has suggested that the hold magnets should be provided with core material which can be permanently magnetized. Then, residual flux will hold the crosspoint operated, and the power drain will not continue throughout the call. Heretofore, however, this use of residual flux to hold a crosspoint has not gained popularity because it has been necessary, in effect, to set-up a new switch path for reversing current and removing the residual flux from the hold magnet cores when the crosspoint must be released.

Accordingly, an object of this invention is to provide a new and improved magnetic latching switch. In this connection, an object is to provide a magnetically latching switch which automatically releases itself when a call is completed. More particularly, an object is to provide a new and improved crossbar switch wherein it is not necessary to maintain a continuously energized hold magnet while a call is in progress.

In keeping with one aspect of this invention, these and other objects are accomplished by a switching network comprising a plurality of crossbar switches, each having select and hold magnets. The magnetic characteristics of the hold magnet are such that its core flux is driven into magnetic saturation responsive to an operating pulse of one polarity applied across the magnet windings. Thereafter, at least one of the crosspoints controlled by that magnet is held by the residual core flux until the call is terminated. Responsive thereto, a release voltage pulse of reverse polarity is applied across the winding of the hold magnet to drive its core flux into an unsaturated state, and the crosspoint is released.

The above mentioned and other features of this invention and the manner of obtaining them will become more 3,400,225 Patented Sept. 3, 1968 apparent, and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a drawing of a sleeve circuit in a crossbar switch; and

FIG. 2 is a hysteresis loop which helps explain how the crosspoints operate.

As those skilled in the art know, a crossbar switch comprises a rectangular frame having mechanical and electrical components mounted thereon. The mechanical components comprise a coordinate array of parallel bars or shafts which are rotatably mounted by means of suitable bearings, leaf springs, or the like. The bars running in one direction are called select bars, and those running in a perpendicular direction are called hold bars. Magnets are positioned on the frame near the ends of the bars to control the rotation thereof. First, the select magnet operates, and then the hold magnet operates. Thereafter, the select magnet releases and the hold magnet remains operated for the duration of the call.

Distributed along the length of each of the select bars are a number of wire spring fingers which swing with the bar, either clockwise or counterclockwise, when the bar is rotated. If a select bar is rotated first and then a coordinate hold bar is thereafter moved, the wire spring finger at the crosspoint where the two bars intersect is bent to push against and close a set of electrical contacts. These contacts are held closed as long as the hold magnet is operated.

The electrical components comprise a plurality of bare wires running through the entire length of the switch in parallel with the hold bars. These wires are called verticals. Perpendicular to the bare wires and extending in the third dimension, with respect to the coordinate axes of the select and hold bars, are contact spring stack-ups, called crosspoint sets. These springs are the electrical contacts which move when the finger pushes them to a closed position. They then touch their associated bare wire verticals and complete a current carrying contact.

Among the crosspoint contacts are control contacts, sometimes called sleeve contacts. When a path is set up, a sleeve connection is extended through these sleeve contacts in parallel with the voice path. Since the hold magnets are normally energized (via a circuit including the sleeve connection) for the duration of the call, the line circuits on each end of the voice path supply a sleeve potential which can be removed to drop the path. This is the potential which causes the constant power drain that is avoided by the invention.

FIG. 1 shows a sleeve connection, as it is used in this invention to control the residual magnetism in the cores of the hold magnets of a completed path. In greater detail, this sleeve connection extends through a line circuit 100, three cascaded crossbar switching stages 101-103, and a talking battery supply trunk circuit 104. Since each of these circuits -104 may take any well known form, no details are given for them. The subscriber line circuit 100 is here shown as having a battery 105 and a cut-oft" relay 106 connected in series with the sleeve. The trunk circuit 104 has a sleeve relay 107 and a supervision relay 108. Cut-oil, sleeve, and supervision relays are well known to those skilled in the art and nothing further need be said about them.

Each of the switching stages has a bare wire vertical, as at 109, which is cut at 110 to provide two electrically isolated sets of contacts. When a crosspoint closes, all of the contacts thereat operate simultaneously to touch and make an electrical connection with the bare wire vertical. The crosspoint of switch 101, for example, is closed by a hold magnet which is operated via lead 116 extending to a conventional marker (not shown). All other crosspoints are constructed and held in a similar'manner.

To set up a connection, the marker selects the operate 7.

This drives the flux of the core of magnet 115 to saturation. The same thing happens in each of the stages 102 and 103 to operate and saturate the hold magnets 117, 118. After the pulse ends, the marker maintains a ground potential on the operate leads, such as 116.

The described operation closes a switch path includ-' ing talking conductors 120, and a parallel sleeve connection. The sleeve connection may be traced from battery 105 through the winding of the cut-off relay 106 and contacts 121-132 (in numerical order) to the winding of the sleeve relay 107 and then to negative battery. Relays 106 and 107 operate in response to the ground supplied by the marker. Closure of the talking path causes the operation of supervisory relay 108 in any well known manner. Contacts 133, 134 close and ground is applied over the path including contacts 121132 to hold the cut-off relay 106 in an operated condition. Thereafter, the marker releases. The selection of hold magnets, operation of the sleeve and cut-off relays, and release of the marker are conventional. The unique feature is the saturation of the magnet cores to provide a residual magnetism for holding the closed crosspoint switch path without continuous current drain.

During the conversation, the sleeve is clamped to the ground potential at contacts 134. Thus, no stray potentials which normally could be expected will provide enough energy to release the switch path.

After the call is over and the subscribers hang up, the supervisory relay 108 releases in a known manner and ground is removed from the sleeve lead at contacts 134. A current then fiows from negative battery through the winding of the sleeve relay 107, contacts 132, 131 and the winding of the hold magnet 118 to ground for a period of time which is long enough to drive core flux away from saturation. In like manner, a current flows from negative battery 105 through the winding of the cut-off relay 106, contacts 121, 122, and the winding of the hold magnet 115 to ground for driving its flux away from saturation. Magnets 115, 118 release.

Magnet 117 may or may not release depending upon minor variations of the characteristics of the individual hold magnets. Actually, it makes no difference whether the center magnet does or does not release at this time.

The marker is adapted to apply a negative test potential to the operate leads to determine whether the hold magnets are busy. Thus, a negative potential will appear on the lead 140 before the hold magnet 117 can again be energized by an operating potential. Since the sleeve clamping potential is not present at the contacts 134 when the busy test is made on an idle vertical, this negative test potential is adequate to drive core flux into an unsaturated state and thereby release the crosspoint of the switch 102.

FIG. 2 is a hysteresis loop which illustrates one manner in which the magnetic characteristics may be provided for. The coil winding has a number of high impedance turns, some of which may be coupled through a diode to cause a unidirectional magnetic effect having a greater magnetic saturating effect when current flows one way than when it flows another way. An alternative construction would use a combination of hard and soft core materials in a series magnet field to give the desired unidirectional saturation characteristics. In any event, the hold magnet coil and core combination may be designed to produce an asymmetrical magnetic effect which facilitates latching responsive to current in one direction and unlatching responsive to current in an opposite direction. This will add a degree of reliability since the crosspoint will not tend to latch if driven too far toward unsaturation.

complished by the application of 48 v. negative through the relay windings, whereas the marker operates the magnets with a surge which has a maximum potential of about v. positive. This, too, adds reliability.

The advantages of the invention are two-fold. First, there is no need for a current drain to keep the hold magnets energized for the duration of the call. Second, there is no need for re-selecting the magnetically latched hold magnets when'a call is ready to be released. The magnetically latched crosspoints are released as quickly and easily as conventionally held switch paths are released.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.

I claim:

1. A switching network comprising a plurality of cascaded crossbar switches, means in each of said switches for holding the crosspoints of said switch after operation thereof, said means comprising at least one electromagnet having a core with a winding thereon, means including a sleeve conductor extending through a cascaded series of crosspoints for supplying a potential to one side of the windings of each of said holding magnets, means for selectively applying a pulse of a first polarity to the other side of said windings for operating at least one of the crosspoints associated with the energized winding, said pulse driving the flux of the core associated with the energized winding into magnetic saturation, and means responsive to the termination of a call for applying a voltage of second polarity to each end of the sleeve conductor for energizing the windings connected thereto to drive said cores of said energized windings into an unsaturated condition.

2. The network of claim 1 and means for clamping said sleeve conductor to a fixed potential after the application of said pulse of first polarity, said fixed potential precluding a voltage change across the windings con nected to said sleeve while a path is extended through said network.

3. The network of claim 2 and means for conducting busy tests to determine whether said crosspoints are busy or idle before the application of said selective energization of said first polarity pulse, said busy test comprising an application of a pulse of said second polarity, whereby said core flux is driven to said unsaturated condition if said fixed clamping potential is not present.

4. A magnetically latching crossbar switch comprising a coordinate array of select and hold bars, means associated with each of said hold bars for holding operated the crosspoints of said switch, said means comprising at least one hold magnet having a core with a winding thereon, contact means at each of said crosspoints including a sleeve contact for extending switch paths through said switch, means comprising said sleeve contacts for supplying a potential to one side of the hold magnet windings which are associated with the crosspoints having the sleeve contacts through which the potential is supplied, means for selectively applying a pulse of a first polarity to a selected one of said windings for operating the associated crosspoint, said pulse saturating the core associated with the energized winding to hold a crosspoint operated, and means for thereafter applying a voltage of second polarity to energize the windings connected to the sleeve contact of an operated crosspoint for driving said core into an unsaturated condition and thus release said crosspoint.

5. The network of claim 4 and means for clamping the potential on the side of said winding connected to said sleeve contact when the crosspoints controlled by the magnet are busy, said potential precluding a voltage change across said winding while a path is in service.

6. The network of claim 5 and means for conducting busy tests to determine whether said crosspoints are busy or idle before said selec ve energization by said first polarity pulse, said busy test comprising an application of a pulse of said second polarity across said winding, whereby said core flux is driven to said unsaturated condition if said clamping potential is not present.

7. A switching network comprising a plurality of cascaded crossbar switches, magnetic core means in each of said switches, means for saturating said cores for holding the operated crosspoints of said switch without requiring a continuous current drain, means including a sleeve conductor extending through a cascaded series of crosspoints for supplying a clamping potential to the latching means while crosspoints are operated, means respon- References Cited UNITED STATES PATENTS 10/1955 Johnson 179l8.7 11/1963 Hayward 17918.7

KATHLEEN H. CLAFFY, Primary Examiner.

LAURENCE A. WRIGHT, Assistant Examiner. 

